File Extension


  • Distinguishes a file’s format for the application used to create the file and can be used to simplify the process of locating data. 1
  • A tag of three or four letters, preceded by a period, which identifies a data file’s format or the application used to create the file. File extensions can streamline the process of locating data. For example, if one is looking for incriminating pictures stored on a computer, one might begin with the .gif and .jpg files.  2
  • The last (typically 3 characters) following a period in a file name that indicates what kind of file it is. MS word documents typically end with “.doc,” etc. File extensions are used by the operating system to determine the default application to use to open a file.
  • In DOS and some other operating systems, one or several letters at the end of a filename. Filename extensions usually follow a period (dot) and indicate the type of information stored in the file. For example, in the filename LETTER.DOC, the extension is DOC, which indicates that the file is a word processing file.


  1. Vinson & Elkins LLP Practice Support, EDD Glossary.
  2. Kroll Ontrack, Glossary of Terms
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